I'm not sure if it's really a bug, or just a design flaw (IMHO).. but here goes.

One network I go on has nick services.. and will change your nick to Guest1235235 or whatever if you don't identify. Well obviously I should setup something to auto-identify, but that's not the issue. So anyways.. my nick got changed to Guest1234234 which changed my main nick to that for mirc in general, and my alt. nick to vcv.

However, this is still not the issue, although this is quite annoying.

So.. I change my main nick in options to vcv and alt nick to zephyr (my nick on all the networks at the time is vcv). I click OK.. and for some reason, mIRC changes my nick on the active network to zephyr. I do not see how this makes any sense.. and it is quite annoying.. has happened to me many times now.

This was actually a feature that was added in one of the versions. Previously, the Nickname field was disabled completely while you were connected. Now changing it is supposed to change your nickname where you are (for people that don't know the /nick command). If you want to change your default name, perhaps you should open another server window instead of changing the nickname while you are on the network that you don't want to use that nickname on.

Try re-reading my post, you apparently don't understand it.

Personally, i think the question was answered per your wording. You stated you disliked the "feature" that mirc changes your name when altered in the options field. A user explained why this is so. Maybe you need to reword the question so others can get the idea also?